Electric blasting cap



'June 29 ,1926.

1,590,364 --H. 1.. GRANT "ELECTRIC BLASTING CAP Original Filed July 22. 1925 a n-uc u toz flarryL. Grant,

Patented June 29, 1926.

' UNITED STATES 1,590,364 PATENT OFFICE.

HARRY L. GRANT, OF TAMAQUA, PENNSYLVANIA, ASSIGNOR TO ATLAS POWDER COM- IE'ANY, OF WILMINGTON, DELAWARE, A CORPORATION OF DELAWARE.

ELECTRIC BLASTIN G GAP.

Original application filed July 22, 1925, Serial No. 45,327. Divided and this application filed December 7, 1925. Serial No. 73,638.

This invention has for its object to provide an electric blasting cap which cannot be prematurely exploded by accidentally, or otherwise, coming in contact with stray electric currents, of any nature, either while being transported or actually used on the job. This application is divisional to my pending application No. 45327.

Many cases have been recorded where loss of life and destruction of property have been caused by premature explosions of dynamite of other commerical explosives. There was a cause for each of these accidents. Cases are on record where a shot has been prepared for firing and which has prematurely exploded, apparently without cause. It is thus seen that the cause for premature explosions is not always visible to an observer. With the ever increasing use of electrical 0 power and electric labor saving appliances in and about coal mines and quarries and construction projects, there is always the possibility of encountering stray electric currents. These currents may be found flowing through moist earth, between the source of supply and bad joints or bonds of trolley rails or on water or steam pipes. age electric blasting cap of present American manufacture can be fired by impressing across the ends of its lead wires an E. M. F. of from one to two volts. Potentials of this order cannot be detected without the aid of electrical measuring instruments. Many tests have been made wherein considerably higher potentials have been recorded and yet could not be detected by moist hands of an observer. Not all of the premature ex plosions have been due to electric blasting caps being exploded by stray currents or accidental contact of same with conductors carrying electric current, but a number of accidents have thus been caused.

Among the objects of my invention is The averacter of that shown in U. 8 Patent 720,073 issued to Schmidt and Kraunischfeldt and my former U. S. Patent1,354,100 in that it is not intended to insulate and mechanically support or prevent separation of the lead wires; this now being accomplished by a. metal fuse head covered by U. S. Patent 1,407,167 issued to Charles C. J essen.

A further object is to provide a fuse head for an electric blasting cap, insulated from the charge in the base of the shell and from the side wall of the metal shell and which can be used in connection with a safety shunt or some means of short circuiting the exposed ends of the lead wires) Vhen this has been done the electric blasting cap cannot be exploded by the electric current so long as the safety shunt is in place. My new electric blasting cap differs in this respect from other types of electric blasting caps, except the match-head'type, and differs from the former match-head type in that the efiiciency of the insulation is not dependent upon special forms of assembly in the manufacture of the caps. a

Further objects and advantages of the in vention will be set forth in the detailed description which now follows:

In the accompanying drawing:

Fig. 1 is a vertical sectional view of an electrical detonator constructed in accordance with the invention, and

Fig. 2 is a view upon an enlarged scale of the electrical fuse head and its insulator.

Like numerals designate corresponding parts in both of the figures of the drawing.

It is common practice to utilize electrical fuse heads, comprising strips 5 and 6 of conductive material, which are held in separated relation by an insulating web 7 of cardboard, paper, or the like. The lead wires 8 and 9 are soldered or otherwise suitably connected at 10 and 11 to the strips 5 and 6, said lead wires being insulated, as in dicated at 12 and 13. A suitable match-head composition 14 is ignited when currentflows in the circuit constituted by wire 8, strip 5, strip 6 and wire 9, it being understood that the lower ends of the strips 5 and 6 are connected by an ignition filament (not shown) which is embedded in the match-head composition.

In carrying out the present invention, I provide a spool-like body 15 of dielectric material, by which the-ignition assembly is 110 held in centered relation within-the shell 16 match-head of the detonator. A rubber gasket 17 surrounds the spool-like body and constitutes a water-proof sealing element between the spool and the inner wall of the shell. The explosive charge 18', which may be a body of mercury fulminate, is of such consistency gasket have been forced downwardly into the shell 16, until the tube 19 is firmly bound between the lower end of. the spool and the upper end of the charge 18, a body of'dielectric and water-proof sealing. material 21 is poured into place and in order that this sealing material may be firmly engaged by the shell in such a way as to resist dislodgment therefrom, the shell is provided with an internal groove 23, into which said sealing material enters.

In practice, I contemplate twisting the outer exposed ends of the lead ,wires into engagement witheach other, directly at the point of termination of the insulation thereon, to thereby create a short circuit at such point of connection. This insures that accidental contact of the exposed ends of the pended claims.

lead Wires with sources of stray electric currents will not result in the flow of current through the fusehead assembly. The tube 19 further insulates the fuse head from the side walls of the metal shell.

An electric detonator constructed as herein shown and described cannot be exploded by stray electric currentnor can it be injuriously affected by moisture. Moisture cannot find its way into the detonator because of the presence of the,gasket 17.

It 'is to be understood that the invention is not limited to the precise construction.

set forth'but that it includes within its pur- VieW whatever changes fairly come within either the terms or the. spiritpf the ap- Having described claim is:

1. An electric detonator comprising a shell, an explosive charge in the lower end my invention, what of said shell, an electrical fuse head assembly, a centering'means for said fuse head v assembly comprising a body of dielectric material fitted snugly within the shell and a tube of insulating material between the body of dielectric material and the charge and engaged by both of them and into the open interior of which the lower end of the electrical fuse head assembly projects, the exposed port-ions of the fuse head assemblywithin the said open interior of the tube being coated with. a dielectric material.

2. A device of the character described comprising a shell, an electrical fuse head assembly, a body of dielectricmaterial of spool-like form through which the fuse head assembly projects andwhich body fits snugly within the shell, a water-proof gasket surrounding said body and fitting snugly within the shell and a charge within "the shell below the said body.

3. A structure as recited in claim 2 in combination with an insulating tube fitting snugly within the shell and having its upper end engaged by the spool-like body and its lower end resting upon the charge and a bodyofsealing material within the shell, outwardly of said spool-like body.

4. A unit for an electric detonator comprising an electrical fuse headassembly, a body of dielectric material of spool-like form through which said head assembly passes and a gasket of compressible, waterproof material extending about the circumference of said spool-like body.

5. A detonator comprising a shell, an explosive charge therein of permanent form, a tube of insulating material fitting snugly within the shell and resting upon said charge, a fuse head assembly, a spool-like body of dielectric material through which i said fuse head assembly passes, and -a packingelement-surrounding the spool-like body and forminga water tight joint between the same and the wall of the shell, the lower end of said fuse head assembly projecting be-f yoiid said body and lying within said tube and a body of sealing material .within the shell, outwardly of the spool-like body andbearing upon said SPOOlrlikG body.

6. A structure as recited in claim 5, in combination with a compressible water-proof 10 (gasket surrounding the spool-likebody and fitting snugly within said shell.

In testimony whereof he affixes his signature.

HARRY L. GRANT. 

